Thelarche, also known as breast budding.

Thelarche is the onset of secondary breast development, which often represents the beginning of pubertal development.

It is the stage at which male and female breasts differentiate due to variance in hormone levels.

Thelarche typically occurs between the ages of 8 and 13 years.

The initial growth of breast tissue occurs during fetal development regardless of sex.

Menarche in females is experienced about 2 years after thelarche has begun.

Complete breast development from thelarche to adult breasts, takes  between 2 and 4 years.

Puberty is considered delayed if breast development does not start before age 13 or if a female has not had her first period menarche within 3 years of thelarche.

Secondary breast development occurring before the age of 7 or 8 years could be a sign of premature thelarche or precocious puberty. 

For some girls transient thelarche will occur, with subsequent regression of breast development, and then months or years later, normal breast growth will commence again accompanied by normal pubertal changes.

Pubertal changes, are assessed using the Tanner Scale (Sexual Maturity Rating Scale): stage 1 represents the lack of breast development, stage 2 is the breast budding or thelarche stage, stages 3 and 4 are continual breast growth and areolar development, and stage 5 signifies completion of development.

The growth and accumulation of adipose tissue in the breasts are induced by estrogen.

The development of mammary glands and areolae are caused by progesterone.

Due to change in hormone levels, young breasts are likely to develop asymmetrically and in many cases, adult breasts will remain unequal in size or shape.

Age of thelarche has been decreasing in the past few decades. 

The age of thelarche has decreased at a rate of 0.24 years per recent decade.

Factors that may be contributing to this change in the onset of thelarche include: increasing BMI, changes in pubertal timing, and environmental exposures.

Associations exist between the average age of thelarche and race.

The average age of thelarche for African American females in the United States is between 8.9 and 9.5 years, the average for Causasians is 10-10.4 years, and the average age of thelarche for Hispanic females is approximately 9.8 years.

In African American and Mexican American girls, breast development may occur earlier than in other ethnic groups.

Obesity is associated with an earlier average age of thelarche.

The prevalence of premature thelarche has been increasing over the past several years which many attribute to pesticides.

Premature thelarche is a benign condition in which a young female has breast development before the age of 8 without any accompanied pubertal changes.

Isolated premature thelarche is not associated with menstruation, pubic hair growth, or the bone growth characteristic of puberty.

Initial breast development can be bilateral or unilateral.

Initial breast development usually begins with a firm area of tissue under the areola.

Initial breast development is often tender and palpation is sometimes painful.

 No breast discharge is present.

In 90% of patients with isolated premature thelarche, breast enlargement will resolve 6 months to 6 years after diagnosis.

The most common ages for isolated premature thelarche is between the ages of 0 and 2 years with a prevalence rate between 2.2 and 4.7 percent of all female infants.

Typically with premature thelarche there is alternating progression and regression patterns of growth in 6-week intervals, often completely decreasing in size within 1.5 years.

Premature thelarche does not require treatment.

Precocious puberty is a condition where children undergo puberty before the age of seven or eight years, and differs from premature thelarche in that the individual experiences additional aspects of puberty including menarche, adrenarche, pubarche, vaginal discharge, and bone growth.

An estimated 14 to 18 percent of females who exhibit premature thelarche will additionally develop precocious puberty.

Thelarche variant, is an intermediate condition between premature thelarche and precocious puberty.

Pubic hair growth and advanced bone growth are often present in thelarche variant, but does not result in complete sexual maturity as occurs with precocious puberty.

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